Stair climbing is recognized as a particularly effective type of aerobic exercise, and as a result, exercise machines facilitating this type of exercise are becoming increasingly popular.
There have been a variety of approaches taken in designing stair climbing apparatus, including the simulation of an actual staircase as illustrated in U.S. Pat. Nos. 3,497,215 and 4,687,195. Another approach has been to simulate the action of stair climbing by using a pair of reciprocating pedals.
An example of the later approach is described in U.S. Pat. No. 5,135,447 issued to Robards, Jr. et al. on Aug. 4, 1992 (the disclosure of which is hereby incorporated by reference in its entirety). Other examples of this type of machine are described in U.S. Pat. Nos. 3,316,819, 3,529,474, 3,628,791, 3,979,302, 4,496,147, 4,600,187, 4,676,501, and 4,720,093.
As exemplified by U.S. Pat. No. 5,135,447, these machines includes a pair of pedals which are adapted for vertical reciprocating motion to provide a user who is standing on the pedals with a simulated climbing exercise. The vertical reciprocating motion is typically translated into a rotary motion by a suitable system of belts, gears and clutches, for example.
The rotary motion (which may be imparted to a shaft, flywheel or the like) is opposed by a variable source of resistance force, typically an alternator, eddy current break or the like. The alternator is responsive to a control signal for selectively varying the level of resistance. When the user's rate of exercise reaches a predetermined threshold, the control signal causes the resistance to sharply increase. The higher resistance compels the user to decrease his or her rate of exercise. In this manner, variable resistance devices such as alternators have been used to control the rate of user exercise. The rate of user exercise is also controlled by prompting the user to pedal faster or slower. Consequently, variations in exercise intensity are achieved by varying the rate at which the user steps.
In general, the objective of these systems is to simulate stair climbing. Stair climbing is characterized by its uniform, repetitive nature. Ideally, stair climbing apparatus would provide a more dynamic climbing simulation to increase user interest.